1. Field of the Invention
The present invention relates to a sealing material for sealing an end portion of a rotary body, such as an image carrier, designed for use in electrophotographic image formation, to a usage of the sealing material, and to a developing apparatus.
2. Description of the Related Art
Conventionally, an electrophotography-based image forming method as shown in FIG. 9 has been adopted in a wide range of image forming apparatuses including a printer, a copying apparatus, and a facsimile apparatus. Electrophotographic image formation is carried out as follows. As a developer, fine-grained colored powder called toner is used. With the toner, an electrostatic latent image formed on a surface of a photoconductive drum 1, acting as an image carrier, is visualized, thus achieving development. On the surface of the photoconductive drum 1 is formed a photoconductive layer made of a photoconductive insulating substance, which normally exhibits electric insulation but exhibits conductivity when exposed to light. The photoconductive drum 1 is rotated in a rotation direction 1a, namely, in a clockwise direction as viewed in FIG. 9. To bring the surface of the photoconductive drum 1 into an electrically charged state, a charging device 2 is provided. Arranged on the downstream side of the charging device 2 along the rotation direction 1a is a developing apparatus 3. On the downstream side of the developing apparatus 3, a recording sheet 4 is supplied in contact with the photoconductive drum 1, and below the recording sheet 4 is arranged a transfer device 5. Arranged on the upstream side of the charging device 2 is a cleaning device 6. The recording sheet 4 is, after making contact with the photoconductive drum 1, conveyed to a fixing device 7, and is then heated and pressurized by a heating roller 8 and a pressure-applying roller 9.
When light irradiation 10 is carried out on the surface of the photoconductive drum 1 uniformly charged by the charging device 2, an electrical charge remaining in the region exposed to light disappears, whereupon an electrostatic latent image is formed. The light irradiation 10, in the case of a laser printer for example, refers to application of beams of laser light whose luminescence intensity has been modulated in accordance with an image to be recorded, or, in the case of a copying apparatus, refers to application of light reflected from an surface of an original. The developing apparatus 3 supplies toner, i.e. charged powder of developer, to visualize the electrostatic latent image formed on the surface of the photoconductive drum 1. The toner has a highly insulating property. When corona discharging is conducted by means of the transfer device 5 so as for the toner to be charged with a polarity reverse to that of the toner, the toner deposited on the surface of the photoconductive drum 1 is sucked, and is then transferred to the surface of the recording sheet 4. The toner transferred onto the recording sheet 4 is, after being molten once under the heat and pressure applied by the fixing device 7, fixed to the surface of the recording sheet 4. The residual toner remaining on the surface of the photoconductive drum 1 is removed by the cleaning device 6, so that charging is performed by the charging device 2 without causing any inconvenience.
In the developing apparatus 3, toner 12 stored in a casing 11 is supplied, via a developing roller 13 placed in contact with the photoconductive drum 1, to the photoconductive drum 1. In order for the toner 12 within the casing 11 to be efficiently deposited on the surface of the developing roller 13, a supply roller 14 is provided. The supply roller 14 allows the toner 12 within the casing 11 to be agitatedly conveyed toward the developing roller 13 while making contact with the developing roller 13. A blade 15, acting as a developer regulating member, controls the amount of toner in such a way that the thickness of the toner layer, deposited on the outer circumference of the developing roller 13 rotating with respect to the casing 11 of the developing apparatus 3, is kept within a predetermined range. To charge the toner 12, DC power sources 16a and 16b are provided. The DC power sources 16a and 16b are so designed that a voltage to be applied to the supply roller 14 is higher in terms of absolute value, to allow the toner 12 to move smoothly from the supply roller 14 to the developing roller 13.
In the developing apparatus 3, although the toner 12 is supplied from the developing roller 13 to the photoconductive drum 1, part of it may possibly find its way into opposite sides of the developing roller 13, as viewed in a rotary axial direction thereof. To permit rotation, a rotary shaft of the developing roller 13 is supported with a gap left that is large enough to allow passage of fine-grained colored powder of toner 12. If the toner 12 is leaked from such a rotation supporting portion, the interior of the image forming apparatus gets soiled with the toner 12, resulting in a waste of the toner 12. To prevent leakage of the toner 12, a seal is provided around the opposite ends of the outer circumferential surface of the developing roller 13 in the rotary axial direction, and also around the rotary shaft.
In cases where one-component toner is used as a developer which is supplied from the developing apparatus 3, the blade 15 plays an important role in regulating the thickness of the toner 12 deposited onto the outer circumferential surface of the developing roller 13. Inconveniently, the toner 12 tends to enter, through the end portion of the blade 15, around the axial opposite sides of the developing roller 13. Intrusion of the toner 12 through the end portion of the blade 15 impairs the thickness-regulating effect brought about by the blade 15. Thus, to prevent intrusion of the toner 12 through the end portion of the blade 15, a sealing material needs to be additionally provided.
FIG. 10 illustrates the developing roller 13, with its one axial end kept in a sealed state. Note that the other axial end thereof is also kept in the same state. Specifically, a shaft 17 of the developing roller 13 is rotatably supported, at its axial opposite ends, in the casing 11 by a bearing 18. Provided at each of the opposite ends of the outer circumferential surface of the developing roller 13 is a side seal 19. The side seal 19 serves to prevent the toner 12 from leaking from the bearing 18, provided at the side wall of the casing 11, to the outside. In FIG. 9, for sake of simplicity, the blade 15 is shown as being one part of the casing 11. In reality, however, the blade 15 is provided independently of the casing 11, and is attached via a fitting plate 20 to the casing 11. The fitting plate 20 is fixed to the casing 11 with a bolt 21. On the rear side of the blade 15's end portion is provided a blade rear seal 22. The side seal 19 corresponding to the developing roller 13 and the blade rear seal 22 corresponding to the blade 15 partly overlap each other. A gap tends to be created in a seam between these seals.
FIGS. 11A and 11B illustrate the sectional configuration taken from the right-hand side of FIG. 10, with FIG. 11A showing a sectional view taken along line A—A of FIG. 10, and FIG. 11B showing a sectional view taken along line B—B of FIG. 10. As shown in FIG. 11B, a gap tends to be created in the seam between the side seal 19 and the blade rear seal 22, causing leakage of toner.
FIGS. 12A and 12B are views of the casing 11 incorporating the developing roller 13, the side seal 19, and the blade rear seal 22, and an assembly obtained by fitting the blade 15 to the fitting plate 20, illustrating how the latter is mounted in the former. FIG. 13 is a view of the casing 11 incorporating the side seal 19 and the blade rear seal 22, the assembly obtained by attaching the blade 15 to the fitting plate 20, and the developing roller 13, illustrating a state in which the assembly and the developing roller 13 are separated from the casing 11. FIGS. 14 and 15 illustrate the contours of the side seal 19 and the blade rear seal 22 in an unmounted state, respectively, with FIGS. 14A and 15A showing the front face, and FIGS. 14B and 15B showing the right-hand face. The side seal 19 has a double-layer structure: a layer made of a felt 19a formed on its top surface; and a layer made of a sponge-like elastic foamed material 19b formed on its back surface. Since the side seal 19 is placed in contact with the outer circumferential surface of the developing roller 13, the sliding resistance needs to be reduced. To achieve this, the felt 19a layer is provided on the top surface of the side seal 19.
Conventionally, an end portion of a rotary body has been sealed with a felt, a sponge, a sealing material obtained by laminating together a felt and a sponge, a pile-like sealing material, or the like. To achieve sealing satisfactorily, a sealing material in use is required to exhibit excellent adhesiveness with respect to the rotary body. In light of this, sealing against leakage of powder is conducted by strong compression or application of heavy pressing force. By so doing, the adhesiveness with respect to the rotary body can be enhanced, thereby preventing intrusion of powder into the sealed portion. In this case, however, an unduly large torque is developed in the rotary body, and this causes an excessive load in the rotary body, which is detrimental to the working life of the machine. Furthermore, during high-speed rotation, the friction between the sealing material and the sliding portion of the rotary body is undesirably increased, with the result that the roller suffers from quality degradation due to a temperature rise caused by frictional heat, and that the powder particles, if made from a resin material, soften due to the frictional heat and consequently stick together.
As shown in FIG. 9, in electrophotographic image formation, development is achieved by forming an electrostatic latent image on the photoconductive drum 1 acting as an image carrier, followed by selectively supplying charged toner from the developing apparatus 3. Therefore, not only the developing roller 13 rotating in the developing apparatus 3, but also the photoconductive drum 1 need to be subjected to sealing against toner leakage. In the cleaning device 6 in particular, the residual toner remaining on the outer circumferential surface of the photoconductive drum 1 must be removed thoroughly. Prior art techniques concerning sealing of a cleaner equivalent to the cleaning device 6 have been disclosed for example in Japanese Examined Patent Publications JP-B2 4-41350 (1992) and JP-B2 4-41351 (1992). Also in these prior art techniques, a sealing material is provided separately for a rear end portion of a cleaning blade and an end portion of an image carrier, and a felt or an elastic foamed material is used for forming the sealing material.
In sealing an end portion of a rotary body, such as the photoconductive drum 1 and the developing roller 13, for use in electrophotographic image formation, an enhancement of adhesiveness cannot be achieved without increasing the torque of the rotary body. An unduly large torque is detrimental to the working life of the machine. By contrast, if sealing is conducted under a light load to reduce the torque, the sealability is deteriorated, and thus powder particles enter the sealed region. As a result, the powder particles undesirably fall in drops or are scattered around. Furthermore, during high-speed rotation, the rotary body undergoes a sharp temperature rise because of heat caused by the friction between the sealing material and the rotary body. As a result, the powder particles, if made from resin, tend to soften and consequently stick together. To overcome such a drawback, it is necessary to make a structure for supporting the rotary body complicate and thus increase the number of constituent components.
As shown in FIG. 10, although the developing roller 13 has its side part sealed with the side seal 19 to prevent leakage of the toner 12, it is not likely that perfect sealing can be achieved in this manner. If leakage of the toner 12 occurs, the toner 12 filled in the casing 11 shown in FIG. 9 runs out quickly, resulting in an undesirable increase in the running cost. Furthermore, the periphery of the developing apparatus 3 is prone to getting soiled with the leaked toner 12. To avoid this, it is necessary to provide an additional component such as a cover for preventing the toner 12 contamination from spreading widely.
Preferred examples for forming the conventional side seal 19, i.e., a material for sealing the end portion of the developing roller 13, include a felt, a sponge, a sealing material obtained by laminating together a felt and a sponge, and a pile-like sealing material. For example, in the developing apparatus 3, in the case of using a felt, a felt made of polytetrafluoro ethylene, such as “Teflon” (trademark) having improved slidability is used, and, in the case of using a sponge, a silicon sponge having high hermeticity is used. However, to obtain high adhesiveness with respect to the developing roller 13, sealing against leakage of the toner 12 is conducted under strong compression or application of heavy pressing force. This leads to an increase in torque required for rotatably driving the developing apparatus 3, resulting in occurrence of abrasion and banding in the drive-transmission mechanism. By contrast, if the sealing is conducted under a light compressive force, the toner 12 finds its way into the side seal 19, and thus the interior of the apparatus gets soiled with the fall or scattering of the toner 12. As a result, the printing quality is degraded.
Regarding sealing of the blade 15, acting as an end-portion developer regulating member, and the developing roller 13, since there is a difference in level between these two components, to achieve satisfactory sealing, a plurality of sealing materials, including the side seal 19 and the blade rear seal 22, have hitherto been used to seal the end portion of the developing roller 13 and the rear surface of the blade 15 acting as an end-portion developer regulating member. Moreover, the sealing materials are put under strong compression. This leads to an increase in torque required for driving.
In the case of using a fibrous sealing material, if the sealing material is made of yarns of thick fiber in consideration of permanent deformation, its elasticity becomes high, and the torque required for driving is increased, resulting in a rise in the manufacturing cost. By contrast, if the sealing material is made of yarns of thin fiber, sufficient elasticity cannot be attained, resulting in the sealing material being leaky.
Further, in the conventional sealing material, when a sealing pressure is applied to obtain adequate sealability, heat is undesirably produced due to the friction between the developing roller 13 and the side seal 19's surface during high-speed rotation. Because of the resultant frictional heat, the toner 12 softens or is molten, and consequently the developer particles stick together.